1. Field of the Invention
This invention relates to simplified sound reproducing apparatus, and in particular, to a toy phonograph wherein the mechanical vibrations set up in a reproducing stylus by the undulations in a record groove are transmitted, without conversion into electrical signals, to a diaphragm to cause same to emanate the corresponding sound waves. Even more particularly, the invention pertains to an improved mechanism for automatically returning the pickup arm of such a phonograph to a predetermined starting position on the perimeter of the record upon completion of playback.
2. Prior Art
In a well known example of toy phonographs having a battery-powered electric motor for driving a turntable, the motor is manually switched on when the pickup arm is in a predetermined starting position on the record on the turntable and, the motor is automatically switched off when the pickup arm reaches a predetermined terminal position on the record upon completion of playback. The pickup arm is spring returned to the starting position only when its stylus is manually disengaged from the groove in the record, as, for example, by the depression of a push button. Thus, unless the push button is depressed upon completion of playback, the pickup arm is held in the terminal position with its return spring in a state of maximum loading.
In order to overcome this defect, and to cause automatic return of the pickup arm from the terminal to the starting position, it has been suggested in the prior art to fixedly mount a cam on top of the record on the turntable for simultaneous rotation therewith. The cam is substantially cylindrical or disc-like in shape, with its top so-shaped as to provide a sloping edge along the circumference. As the pickup arm reaches the terminal position on the record upon completion of playback, a cam follower is thereby urged to ride onto the rotating cam at its lowest point and is subsequently raised to cause the pickup arm to have its stylus-carrying end lifted away from the record and, then, to be spring returned to the starting position.
This type of automatic pickup arm return mechanism makes the toy phonograph inordinately expensive to manufacture, because its various working parts must be formed to close tolerances and assembled precisely in their predetermined relative positions in order that the cam follower may ride onto the rotating cam at its lowest point when the pickup arm reaches the terminal position on the record. Furthermore, the pickup arm return mechanism of the prior art does not lend itself for use with records having a multiplicity of nested spiral grooves. It should be noted that these deficiencies of the prior art pickup arm return mechanism arise essentially from the fact that the cam is mounted on the record, or on the turntable, for simultaneous rotation therewith.